Abstract

To contrast the phenomenon of HC formation in a Diesel and a spark ignition engine, a chapter is included on the latter. The absorption and desorption of fuel by cylinder lubricating oil films has been modelled using principles of mass transfer in this Chapter. Henry’s Law for a dilute solution of fuel in oil is used to relate gas to liquid phase fuel concentrations. Mass transfer conductances in gas and liquid phases are considered, the former via use of Reynolds’s Analogy to engine heat transfer data, the latter through assuming molecular diffusion through an effective penetration depth of the oil film. Oxidation of desorbed fuel is assumed complete if the mean of burned gas and lubricating oil film temperatures is greater than 100 K. Below this value, the desorbed fuel is considered to contribute to hydrocarbon emissions. Comparison with engine test data corroborates the absorption/desorption hypothesis. The model indicates the equal importance of gas and liquid phase conductance.